Differential detection magnetoresistance head with laminated structure

ABSTRACT

A GMR element part is formed of a laminated structure which comprises at least one pair of ferromagnetic layers and a nonmagnetic intermediate layer interposed between the pair of ferromagnetic layers. Signal magnetic field detecting ferromagnetic layers will be optionally disposed one each outside the pair of ferromagnetic layers. The GMR element part consists of a laminated structure which is provided with one pair of GMR ferromagnetic layers opposed to each other across a nonmagnetic intermediate layer or a laminated structure which is provided with one pair of GMR ferromagnetic layer opposed to each other across a nonmagnetic intermediate layer and at least one low-permeability ferromagnetic layer disposed there between through the medium of a nonmagnetic intermediate layer. The GMR element part functions as a read head for sensing the resistance which is varied when signal magnetic fields of mutual opposite directions are applied to the pair of GMR ferromagnetic layers and displaying a differential detection type output response. A granular type ferromagnetic intermediate layer will be used as the GMR element part.

This is a division of application Ser. No. 08/401,489, filed Mar. 101995, now U.S. Pat. No. 5,828,525 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a magnetoresistance head for use in magneticrecording devices, VTR's, etc. The invention relates more particularlyto a differential detection type magnetoresistance head.

2. Description of the Related Art

In recent years, the trend of recording tracks toward a decreasing widthand that of recording wavelengths toward an increasing frequency havebeen urging magnetic recording devices such as, for example, hard discdevices to use a further improved recording density. When the width ofthe recording track is decreased, the sensitivity of the read head isrequired to be further enhanced because the decrease of the track widthentails a decrease in the amount of signal magnetic flux from themagnetic recording medium. As read heads endowed with such highsensitivity, the magnetoresistance heads (hereinafter referred to as “MRhead”) have been attracting attention.

In the MR heads, the MR heads (GMR heads) of the type using theso-called giant magnetoresistance (hereinafter referred to as “GMR”) andhaving a large rate of change in resistance as compared with the MRheads of the type using the anisotropic magnetoresistance (hereinafterreferred to as “AMR”) are expected to find recognition as magnetic headspromising high read sensitivity in the future.

For the purpose of improving the linear record resolving power with theshield type MR head which currently prevails in the existing MR heads,the interval or gap between the shield layer possessed of highpermeability and the MR element must be decreased. In this case, it isextremely difficult to decrease this interval to or even below 0.1 μm,with maintaining good electric insulation between the shield layer andthe MR element. Thus, the shield type MR head has its limit to theimprovement of the linear record dissolving power.

As a breakthrough, the so-called dual element type MR head which has twoMR elements superposed through the medium of a nonmagnetic intermediatelayer has been proposed. This dual element type MR head generates aso-called differential detection type output response by virtue of thephenomenon that it produces a change in the resistance only when themagnetic recording medium applies signal magnetic fields of oppositedirections to the two MR elements, whereas it produces no change in theresistance when this medium applies signal magnetic fields of one samedirection thereto. The differential detection type MR head has the readresolving power thereof governed by the thickness of the nonmagneticintermediate layer and, unlike the shield type MR head, requires the twoMR elements thereof to be insulated from each other magnetically and notelectrically. The differential detection type MR head, therefore, allowsthe thickness of the nonmagnetic intermediate layer to be notablydecreased, for example, to or even below 10 nm. As a result, it iscapable of reading an unusually high linear recording density.

Among the conventional differential detection type MR heads is countedthe MR head which uses two AMR elements possessing substantiallyidentical magnetoresistance characteristics (MR characteristics). Whenthe AMR elements are used, such operating point bias magnetic fields asrotate their magnetization in opposite directions like about +45° and−45° from the direction of width of the track are applied. Thedifferential detection type MR head can be realized as a result.

It is suspected, however, that the sensitivity obtainable with theconventional differential detection type MR head using AMR elements willprove insufficient in the near future because the inflow of a signalmagnetic field (medium magnetic field) to the upper part of the MRelement is not attained when the thickness of the nonmagneticintermediate layer is decreased. Further, since this MR headnecessitates application of the operating point bias magnetic field ofthe nature mentioned above, it has the problem of encounteringdifficulty in the impartation and the adjustment of the magnetic field.

The differential detection type MR head using AMR elements is generallyconstructed by superposing two AMR layers through the medium of anonmagnetic intermediate layer and forming a pair of electrodes for thesupply of a sense current on the upper AMR layer. For the AMR elementsin this construction, the angles between the currents and themagnetization constitute themselves an important factor. In order toequalize substantially the MR characteristics of the two AMR elements inthe differential detection type MR head, therefore, it is necessary thatthe characteristics of the two AMR layers themselves be rendered uniformand no angle be formed in the directions of sense currents suppliedbetween the two AMR layers. In the case of the construction in which theelectrodes are formed as superposed on one of the AMR layers asdescribed above, the upper and the lower AMR layer produce a differencein the current distribution (as in direction) and the directions ofsense currents between these two AMR layers are liable to form an angle.Even when magnetic fields of identical directions are applied to the twoAMR layers, therefore, the possibility ensues that the resistance willbe varied and this variation will be emitted in the form of a signal.The accidental detection of this erroneous signal possibly results ingeneration of noise.

Since the conventional differential detection type MR head uses two AMRelements as described above, it entails the problem of readily degradingthe sensitivity thereof owing to the fact that the depth of permeationof a signal magnetic field decreases and the fact that the directions ofcurrents between the two AMR layers are inclined toward each other andalso the problem of complicating the impartation and the adjustment ofthe operating point bias magnetic field.

SUMMARY OF THE INVENTION

An object of this invention, therefore, is to provide a differentialdetection type magnetoresistance head which not only possesses improvedline resolving power (read resolving power) but also realizes highsensitivity and high S/N ratio under high reliability.

The magnetoresistance head of the present invention is a differentialdetection type magnetoresistance head which comprises amagnetoresistance element having a laminated structure comprising atleast one pair of ferromagnetic layers and an intermediate layerinterposed between the pair of ferromagnetic layers and formed of eithera nonmagnetic intermediate layer or a granular type ferromagneticintermediate layer separated into a magnetic region and a nonmagneticregion, the magnetoresistance element part permitting the resistancethereof substantially varied when signal magnetic fields of mutuallyopposite directions are applied to the pair of ferromagnetic layers,characterized in that the signal magnetic fields are detected byutilizing the variation of resistance based on the giantmagnetoresistance due to the spin-dependent scattering in themagnetoresistance element part.

The nonmagnetic intermediate layer as used in the present inventionexcludes that which is formed of an antiferromagnetic material as wellas that which is formed of a ferromagnetic material.

The differential detection type MR head of this invention can be broadlydivided into the following three forms. The first form is such that alaminated structure comprising a pair of ferromagnetic layers excellingin the spin-dependent scatting ability (hereinafter referred to as “GMRferromagnetic layer”) and a nonmagnetic intermediate layer interposedbetween the pair of GMR ferromagnetic layers and possessed of lowresistance fit for spin-dependent scattering (hereinafter referred to as“GMR nonmagnetic intermediate layer”) is caused to function as amagnetoresistance element part exhibiting a giant magnetoresistance dueto the spindependent scattering (hereinafter referred to as “GMR elementpart”).

The second form is such that a laminated structure comprising at leastthree ferromagnetic layers and nonmagnetic intermediate layers eachinterposed between the adjacent pairs of the ferromagnetic layers andhaving the ferromagnetic layers each formed of at least two GMRferromagnetic layers and at least one low-permeability ferromagneticlayer having the magnetization thereof not substantially varied by asignal magnetic field is caused to function as a GMR element part.

The third form is such that a granular type ferromagnetic intermediatelayer separated into a magnetic region and a nonmagnetic region iscaused to function as a GMR element part. In this form, the pair offerromagnetic layers which are opposed to each other across the granulartype ferromagnetic intermediate layer are used as ferromagnetic layersfor the detection of a signal magnetic field.

The first form of this invention is desired to generate a ferromagneticcoupling force between the pair of GMR ferromagnetic layers and causethe magnetizations of the two GMR ferromagnetic layers to be arranged insubstantially identical directions with a signal magnetic field in astate of zero. The ferromagnetic coupling force between the two GMRferromagnetic layers can be adjusted to a required magnitude bycontrolling the thickness of the nonmagnetic intermediate layer. Theparallel arrangement of the directions of magnetizations may be attainedby application of a bias magnetic field. The impartation of the biasmagnetic field can be effected by causing a hard ferromagnetic film suchas of CoPt or an antiferromagnetic film such as of FeMn or NiO to bedisposed closely to or superposed on the GMR element part.

Incidentally, in the standard conventional GMR multilayered film whichhas ferromagnetic layers and nonmagnetic intermediate layers superposedalternately and utilizes the antiferromagnetic coupling between theferromagnetic layers, the magnetizations of the ferromagnetic layers areantiferromagnetically arranged with a signal magnetic field in a stateof zero. This GMR head cannot be expected to detect a differentialdetection type signal magnetic field because the magnetizations of theferromagnetic layers are rotated toward ferromagnetic arrangements andthe resistance is consequently varied when signal magnetic fields ofequal directions are applied to all the ferromagnetic layers.

The GMR ferromagnetic layers in the differential detection type MR headof the first form may concurrently serve as ferromagnetic layers for thedetection of signal magnetic fields. The MR head nevertheless is desiredto have a structure such that, apart from the GMR ferromagnetic layers,ferromagnetic layers exclusively used for the detection of signalmagnetic fields are severally disposed outside the GMR ferromagneticlayers. Specifically, a laminated structure of GMR ferromagneticlayer/nonmagnetic intermediate layer/GMR ferromagnetic layer is used asthe GMR element part and ferromagnetic layers for the detection ofsignal magnetic fields are severally disposed outside the GMR elementpart. In this case, the GMR ferromagnetic layers and the ferromagneticlayers for the detection of signal magnetic fields are desired to beexchange coupled.

The ferromagnetic layers for the detection of signal magnetic fieldsmentioned above are desired to be made of a ferromagnetic materialpossessing higher permeability than the GMR ferromagnetic layers.Desirably, a pair of ferromagnetic layers for the detection of signalmagnetic fields be formed protrudingly on the opposed medium surfacesand the GMR element part be made to recede from the opposed surface ofthe medium. Owing to this arrangement, the GMR element part having theaforementioned laminated structure can be made to function as asubstantial gap. In the case of this arrangement, the thickness of theGMR element part is set with due respect to the fact that the GMRelement part functions as a substantial gap. In order to accomplish ahigh recording density of the order of 4 to 10 Gb/in², for example, itis desired to give the GMR element part a thickness which is in theapproximate range of from 10 to 100 nm.

Then, the ferromagnetic layers for the detection of signal magneticfields are desired to be made of a material which has higher resistancethan the GMR ferromagnetic layers, namely a material having resistivityexceeding 100 μΩcm. Owing to the use of this material, the ferromagneticlayers for the detection of signal magnetic fields are enabled toacquire exalted sensitivity because the material is capable ofrepressing the partial sense current flow into the layers. Further, itis advantageous that the ferromagnetic layers for the detection ofsignal magnetic fields be formed of ferromagnetic layers which have alarger thickness than the GMR ferromagnetic layers. In this case, thedetection of signal magnetic fields is facilitated because such adversemagnetic effects as the degradation of permeability due to the exchangecoupling with the GMR ferromagnetic layers can be diminished.

The differential detection type MR head of the first form mentionedabove, unlike the conventional GMR multilayered film, enables themagnetizations of the pair of GMR ferromagnetic layers to assumesubstantially equal directions with the signal magnetic fields in astate of zero as by exerting a ferromagnetic coupling force between theGMR ferromagnetic layers. In the case of a perpendicular magneticrecording medium, for example, since signal magnetic fields of equaldirections are applied to the two GMR ferromagnetic layers when thedifferential detection type MR head departs from the magnetizationtransition region of the magnetic recording medium, the angle formed bythese magnetizations is not varied and substantially no variation occursin the resistance. When at least the GMR nonmagnetic intermediate layersdirectly overlie the magnetization transition region of the magneticrecording medium, signal magnetic fields of mutually opposite directionsare applied to the two GMR ferromagnetic layers and the magnetizationscorresponding thereto are rotated in different directions. As a result,the angle formed by the magnetizations of the two GMR ferromagneticlayers is varied and the resistance is varied largely. Thus, thedetection of recorded information can be attained exclusively with themagnetization transition region of the magnetic recording medium.Particularly, the perpendicular magnetic recording medium of the typewhich produces an abrupt signal magnetic field transition in themagnetization transition region thereof is enabled to attain read backsignals with markedly high resolving power and enjoy generousimprovement of linear recording density.

Thus, the differential detection type MR head of the first form, unlikethe conventional differential detection type MR head using an AMRelement operated by virtue of the resistance which variesproportionately to the angle formed by the current and themagnetization, produces a differential detection by utilizing theresistance variable proportionately to the angle formed by themagnetizations of one pair of GMR ferromagnetic layers instead ofrelying on the directions of currents. It, therefore, can realize thehigh read sensitivity which has never been attained by the conventionalAMR element. As a result, the noise which originates in the mutualinclination of the directions of currents occurring between the two AMRlayers and which has posed a problem to the differential detection typeMR head using the conventional AMR element no longer occurs in thedifferential detection type MR head of the first form. Then, this highread sensitivity can be realized with an extremely simple headstructure.

Further, in the differential detection type MR head of the first form,when ferromagnetic layers for the detection of signal magnetic fieldsare severally disposed outside the GMR element part formed of alaminated structure of GMR ferromagnetic layer/nonmagnetic intermediatelayer/GMR ferromagnetic layer, the GMR element part can be made tofunction as a substantial gap and the gap length, therefore, can beenlarged. As a result, the adaptation of the gap length for the lengthof the magnetization transition region of the magnetic recording mediumand the high read sensitivity can be both fulfilled withoutcontradiction. When the nonmagnetic intermediate layer is made tofunction by itself to function as a gap, the ratio of variation of theresistance in the GMR element part formed of a laminated structure ofGMR ferromagnetic layer/nonmagnetic intermediate layer/GMR ferromagneticlayer will be degraded if the thickness of the nonmagnetic intermediatelayer is increased to or even over 5 nm, for example. The resultpossibly may be that the adaptation of the gap length (of the order offrom 10 to 100 nm) for the length of the magnetization transition regionof the magnetic recording medium and the high read sensitivity will besimultaneously fulfilled with difficulty.

When the resistance of the ferromagnetic layers for the detection ofsignal magnetic fields is higher than that of the GMR ferromagneticlayers, the partial sense current flow to the ferromagnetic layers forthe detection of signal magnetic fields can be repressed and thesensitivity of the ferromagnetic layers can be enhanced. The directrotation of magnetizations by the signal magnetic fields of the GMRferromagnetic layers can be repressed either by forming theferromagnetic layers for the detection of signal magnetic fields with aferromagnetic material having higher permeability than the GMRferromagnetic layers or by causing the GMR element part to recede fromthe opposed surface of the medium. As a result, the gap length can bemore precisely regulated by the thickness of the GMR element partbecause the rotation of magnetizations of the GMR ferromagnetic layersis predominantly governed as by the exchange coupling bias magneticfields with the ferromagnetic layers for the detection of signalmagnetic fields.

As more specific structures of the GMR element part in the differentialdetection type MR head of the second form, (1) a structure having a GMRferromagnetic layer, a GMR nonmagnetic intermediate layer, alow-permeability ferromagnetic layer having the magnetization notsubstantially varied by a signal magnetic field (hereinafter referred tosimply as “low-permeability ferromagnetic layer”, a GMR nonmagneticintermediate layer, and a GMR ferromagnetic layer sequentiallysuperposed in the order mentioned, (2) a structure having a GMRferromagnetic layer, a GMR nonmagnetic intermediate layer, alow-permeability ferromagnetic layer, a nonmagnetic intermediate layercapable of weakening ferromagnetic coupling between adjacentferromagnetic layers (hereinafter referred to as “separating nonmagneticintermediate layer”), a low-permeability ferromagnetic layer, a GMRnonmagnetic intermediate layer, and a GMR ferromagnetic layersequentially superposed in the order mentioned, and (3) a structurehaving a low-permeability ferromagnetic layer, a GMR nonmagneticintermediate layer, a GMR ferromagnetic layer, a separating nonmagneticintermediate layer, a low-permeability ferromagnetic layer, a GMRnonmagnetic intermediate layer, and a GMR ferromagnetic layersequentially superposed in the order mentioned may be cited.

In the structure of (1) mentioned above, the magnetization of thelow-permeability ferromagnetic layer, for example, is effected in thedirection of track width and the magnetizations of the two GMRferromagnetic layers are inclined by angles of about +45° and −45°, forexample, from the direction of track width as by means of a sensecurrent magnetic field with the signal magnetic field in a state ofzero. As a result, the detection of signals with high linear responseregion, low distortion, and high S/N ratio can be carried out. In thestructures of (2) and (3), the two low-permeability ferromagnetic layersare desired to be magnetized in directions substantially perpendicularto the medium surface and differing mutually by 180°. Owing to themagnetization so effected, the magnetization stability of thelow-permeability ferromagnetic layers to resist the signal magneticfields is improved because the low-permeability ferromagnetic layerwhich is magnetized in the direction opposite to the direction in whichthe signal magnetic field is applied is exposed to the leak magneticfield emanating from the other low-permeability ferromagnetic layer inthe direction tending to cancel the signal magnetic field. Thesestructures are further at an advantage in acquiring a linear magneticfield-resistance characteristics in a wide range of magnetic fieldswithout necessarily causing the magnetizations of the GMR ferromagneticfields to be inclined in the directions of ±45°.

For the low-permeability ferromagnetic layers mentioned above, aferromagnetic material having permeability of not more than {fraction(1/10)} of the permeability of the GMR ferromagnetic layer is used.Specifically, hard ferromagnetic materials and semi-hard ferromagneticmaterials are concrete examples of the material answering thedescription. The low-permeability ferromagnetic layers are desired tohave permeability of not more than about 100. For the formation of thelow-permeability ferromagnetic layers, it is particularly desirable touse a ferromagnetic material which excels in the spin-dependentscattering ability and allows impartation of high coercive force andlarge uniaxial magnetic anisotropy. The use of this material for thelayers is not indispensable when any of the following structures isadopted for the layers.

For the purpose of preventing the magnetizations of the low-permeabilityferromagnetic layers from being affected by signal magnetic fields whilekeeping their large resistance variations intact, such structures as areenumerated below may be adopted, for example. Namely, (a) a structure inwhich at least the part of the low-permeability ferromagnetic layers ismade to recede from the opposed surface of the medium, (b) a structurein which the low-permeability ferromagnetic layers are each formed of analternate superposition of a ferromagnetic film and a nonmagnetic filmand the thicknesses of the nonmagnetic films are optimized and, as aresult, a large antiferromagnetic coupling desirably of a couplingmagnetic field of not less than about 80000 A/m, a magnitude larger thanthe signal magnetic field, is enabled by dint of the so-calledRuderman-Kittel-Kasuya-Yoshida (RKKY) exchange interaction to occurbetween the adjacent ferromagnetic films, (c) a structure in whichlow-permeability ferromagnetic layers capable of imparting high coerciveforce and large uniaxial magnetic anisotropy and ferromagnetic filmsexcelling in the spin-dependent scattering ability are superposed, and(d) a structure in which a film adapted for impartation of high coerciveforce and uniaxial magnetic anisotropy to either of the low-permeabilityferromagnetic layers of the construction of (3) is interposed betweenthis low-permeability ferromagnetic layer and a substrate and, at thesame time, a film adapted for impartation of high coercive force anduniaxial magnetic anisotropy to the other low-permeability ferromagneticlayer is used for a separating nonmagnetic intermediate layer destinedto form the foundation for this other low-permeability ferromagneticlayer may be cited.

In the differential detection type MR head of the second form describedabove, when the magnetizations of the two GMR ferromagnetic films arerotated in the same direction in conformity to the signal magneticfields generated in the same direction, the angles formed by themagnetizations relative to the low-permeability ferromagnetic layersopposed to each other across the GMR nonmagnetic intermediate layerincrease on the one GMR ferromagnetic layer side and decrease on theother GMR ferromagnetic layer side. As a result, the signal magneticfields are not detected because the resistance is not variedsubstantially. When the signal magnetic fields are applied in oppositedirections on the two GMR ferromagnetic layers, the angles formed by themagnetizations of the two GMR ferromagnetic layers respectively with thelow-permeability ferromagnetic layers opposed to each other across theGMR nonmagnetic intermediate layer are simultaneously increased ordecreased. As a result, notably large resistance variations are causedby the spin-dependent scattering. In other words, a differentialdetection type signal detection system of high sensitivity using GMRelements can be realized. Likewise, in the differential detection typeMR head of this second form, the current distribution within thelaminated structure avoids exerting an effect on sensitivity or otherfactors because the differential detection is generated by fundamentallyutilizing the resistance which varies with the angles formed by the twomagnetizations.

Further, the gap length can be regulated by the interval between the twoGMR ferromagnetic layers because the part of GMR nonmagneticintermediate layer, low-permeability ferromagnetic layer, and separatingnonmagnetic intermediate layer which intervenes between the two GMRferromagnetic layers has notably small permeability with respect to thesignal magnetic fields. A proper gap length of the order of from 10 to100 nm can be fixed proportionately to the linear recording density asby adjusting the thickness of the separating nonmagnetic intermediatelayer. All the factors mentioned above boil down to a conclusion that adifferential detection type MR head of high sensitivity and high S/Nratio can be realized and the linear recording density can be improvedas well.

In the differential detection type MR head of the third form, a granulartype ferromagnetic intermediate layer which is divided into a magneticregion formed mainly of Co, Ni, Fe, etc., for example, and a nonmagneticregion formed of Cu, Au, Ag, and alloys thereof, for example, is used.As ferromagnetic layers for the detection of signal magnetic fieldswhich are opposed to each other across this granular type ferromagneticintermediate layer, those which are used in the structure of the firstform are used.

In the differential detection type MR head of the third form, since thegranular type ferromagnetic intermediate layer serving as a GMR elementpart is equivalent to a substantial gap, the thickness of the GMRelement part is to be set in consideration of this equivalency. Toattain a high recording density falling in the approximate range of from4 to 10 Gb/in², for example, the thickness of the granular typeferromagnetic intermediate layer is desired to be selected in theapproximate range of from 10 to 100 nm. The granular type ferromagneticintermediate layer and the ferromagnetic layers for the detection ofsignal magnetic fields are desired to be exchange coupled across theinterfaces thereof. In the same manner as in the structure of the firstform, the GMR element part or the granular type ferromagneticintermediate layer is desired to be withdrawn from the opposed surfaceof the medium.

The magnetizations within the granular type ferromagnetic intermediatelayer are desired to assume substantially equal directions with thesignal magnetic fields in a state of zero. The desire is satisfied as byinducing a ferromagnetic coupling force between the pair offerromagnetic layers for the detection of signal magnetic fields orapplying a bias magnetic field thereto. The ferromagnetic coupling forcebetween the pair of ferromagnetic layers for the detection of signalmagnetic fields can be adjusted to a necessary magnitude by regulatingthe state of dispersion of a magnetic region in a nonmagnetic regionwithin the granular type ferromagnetic intermediate layer, specificallyby controlling the interval between the adjacent magnetic regions. Thebias magnetic field can be imparted as required by causing a hardferromagnetic film formed of CoPt to be disposed closely to orsuperposed on or an antiferromagnetic film formed of FeMn or NiO to bedisposed closely to the granular type ferromagnetic intermediate layer.

In the differential detection type MR head of the third form, owing tothe exchange coupling between the ferromagnetic layers for the detectionof signal magnetic fields and the granular type ferromagneticintermediate layer, the magnetization of the magnetic region of thegranular type ferromagnetic intermediate layer gains in susceptibilityto the force exerted in the same direction as the magnetization of theferromagnetic layers for the detection of signal magnetic fields inproportion as the proximity thereof to the ferromagnetic layers for thedetection of signal magnetic fields grows. When the magnetizations ofthe two ferromagnetic layers for the detection of signal magnetic fieldsfall in substantially equal directions (as when signal magnetic fieldsare substantially in a state of zero), the magnetizations of themagnetic region of the granular type ferromagnetic intermediate layerassume uniform directions. When signal magnetic fields of equaldirections are applied to the two ferromagnetic layers for the detectionof signal magnetic fields, therefore, the magnetizations of the magneticregion of the granular type ferromagnetic intermediate layer are rotatedas kept in equal directions because the magnetizations of the twoferromagnetic layers for the detection of signal magnetic fields arerotated as kept in equal directions. As a result, the resistance is notvaried. When signal magnetic fields of opposite directions are appliedinstead to the two ferromagnetic layers for the detection of signalmagnetic fields, the magnetizations of the magnetic region of thegranular type ferromagnetic intermediate layer are rotated in directionsdiffering mutually by 180° near the interfaces with the ferromagneticlayers for the detection of signal magnetic fields proportionately tothe rotation of the magnetizations of the ferromagnetic layers for thedetection of signal magnetic fields. Since the parts of themagnetizations of the magnetic region which deviate from the equaldirections increase, the resistance of the granular type ferromagneticintermediate layer increases. As a result, the differential detectiontype MR head can be realized because the detection of signals isattained only when signal magnetic fields of opposite directions areapplied.

Further, since the granular type ferromagnetic intermediate layer hassmall permeability, it is allowed to function as a substantial gap. Thereading of signal magnetic fields with high sensitivity and highresolution, therefore, is accomplished by adjusting the thickness of thegranular type ferromagnetic intermediate layer to a proper magnitude fitfor linear recording density. Further by causing the granular typeferromagnetic intermediate layer to recede from the opposed surface ofthe medium, the signal magnetic fields which are directly sensed by thegranular type ferromagnetic intermediate layer (GMR element part) growweak and the gap length can be regulated more precisely by the thicknessof the granular type ferromagnetic intermediate layer. In thedifferential detection type MR head of the third form likewise, thecurrent distribution within the laminated structure exerts no adverseeffect on sensitivity and other factors because the differentialdetection is principally implemented by utilizing the resistance whichvaries with the angles to be formed by the magnetizations of themagnetic region of the granular type ferromagnetic intermediate layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating the essential construction ofa differential detection type MR head as the first embodiment of thisinvention.

FIG. 2 is a cross section illustrating one example of the modificationof the differential detection type MR head shown in FIG. 1 by theincorporation of a bias film therein.

FIG. 3 is a cross section illustrating another example of themodification of the differential detection type MR head shown in FIG. 1by the incorporation of a bias film therein.

FIG. 4 is a cross section illustrating yet another example of themodification of the differential detection type MR head shown in FIG. 1by the incorporation of a bias film therein.

FIG. 5 is a cross section illustrating still another example of themodification of the differential detection type MR head shown in FIG. 1by the incorporation of a bias film therein.

FIG. 6 is a perspective view illustrating the essential construction ofa differential detection type MR head as the second embodiment of thisinvention.

FIG. 7 is a diagram illustrating the state of magnetization of thedifferential detection type MR head shown in FIG. 6 with the signalmagnetic field in a state of zero.

FIG. 8 is a perspective view illustrating the essential construction ofa differential detection type MR head as the third embodiment of thisinvention.

FIG. 9 is a diagram illustrating the state of magnetization of thedifferential detection type MR head shown in FIG. 8 with the signalmagnetic field in a state of zero.

FIG. 10 is a diagram illustrating variations of resistance by a signalmagnetic field of the differential detection type MR head shown in FIG.8.

FIG. 11 is a perspective view illustrating the essential construction ofa differential detection type MR head as the fourth em of thisinvention.

FIG. 12 is a diagram illustrating the state of magnetization of thedifferential detection type MR head shown in FIG. 11 with the signalmagnetic field in a state of zero.

FIG. 13 is a perspective view illustrating the essential construction ofa differential detection type MR head as the fifth embodiment of thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, this invention will be further described specifically below withreference to embodiments.

The first embodiment of this invention will be described with referenceto FIG. 1. In a differential detection type MR head 1 shown in FIG. 1, afirst signal magnetic field detecting ferromagnetic layer 3 a adapted tohave the magnetization thereof rotated by a signal magnetic field, afirst GMR ferromagnetic layer 4 a, a GMR nonmagnetic intermediate layer5, a second GMR ferromagnetic layer 4 b, and a second signal magneticfield detecting ferromagnetic layer 3 b adapted to have themagnetization thereof rotated by a signal magnetic field similarly tothe first signal magnetic field detecting ferromagnetic layer 3 a aresequentially superposed in the order mentioned on a substrate 2 tocomplete a differential detection type MR element 6. The first signalmagnetic field detecting ferromagnetic layer 3 a and the first GMRferromagnetic layer 4 a are exchange coupled and the second GMRferromagnetic layer 4 b and the second signal magnetic field detectingferromagnetic layer 3 b are likewise exchange coupled.

A laminated structure consisting of the first GMR ferromagnetic layer 4a, the GMR nonmagnetic intermediate layer 5, and the second GMRferromagnetic layer 4 b constitutes itself a GMR element part 7. ThisGMR element part 7 is otherwise called GMR unit. Further at the oppositeends of the differential detection type MR element 6, electrodes 8 a and8 b for feeding sense current are formed to give rise to thedifferential type MR head 1.

For the first and the second GMR ferromagnetic layer 4 a and 4 b, it isdesirable to use a CoFe alloy, Co, a CoFeNi alloy, etc. which haverelatively low permeability than a NiFe alloy, etc. which have highpermeability. These GMR ferromagnetic layers manifest an excellentspin-dependent scattering ability in the interfaces thereof with the GMRnonmagnetic intermediate layer 5. The GMR ferromagnetic layers 4 a and 4b are desired to have a thickness in the approximate range of from 4 to40 nm. If the GMR ferromagnetic layer 4 a and 4 b have a thickness ofless than 4 nm, a gap length (of the order of 10 to 100 nm, for example)adapted for the linear recording density aimed at will not be easily setin spite of the provision of the signal magnetic field detectingferromagnetic layers 3 a and 3 b, in addition to the decrease in the MRratio. Conversely, if they have a thickness exceeding 40 nm, the ratioof variation of the resistance will be possibly degraded markedly. Thefits and the second GMR ferromagnetic layer 4 a and 4 b are specificallyformed of a CoFe alloy film, a Co film, a CoFeNi alloy film and the likewhich have a thickness of about 10 nm.

For the GMR nonmagnetic intermediate layer 5, a Cu film, a Au film, a Agfilm, and films of alloys formed mainly of these metals which areadapted for the spin-dependent scattering can be used. The thickness ofthe GMR nonmagnetic intermediate layer 5 is desired to be in theapproximate range of from 2 to 5 nm. If the thickness of the GMRnonmagnetic intermediate layer 5 exceeds 5 nm, the ferromagneticcoupling force between the first and the second GMR ferromagnetic layer4 a and 4 b will be possibly decreased and the ratio of variation of theresistance lowered. If the thickness of the GMR nonmagnetic intermediatelayer 5 is less than 2 nm, the ferromagnetic coupling force between thefirst and the second GMR ferromagnetic layer 4 a and 4 b will growexcessively. In this case, there ensues the possibility that themagnetizations of the first and the second GMR ferromagnetic layers 4 aand 4 b will be arranged antiferromagnetically only with difficulty andthe ratio of variation of the resistance will be consequently decreasedwhen magnetic fields of mutually opposite directions are applied tothese layers 4 a and 4 b.

It is generally known that in a GMR multilayered film obtained bysuperposing ferromagnetic layers of Co film through the medium of anonmagnetic intermediate layer, a ferromagnetic coupling force and anantiferromagnetic coupling force periodically act between the adjacentferromagnetic layers proportionately to the thickness of the nonmagneticintermediate layer. Generally, in the case of applying such a GMRmultilayered film a shield type MR head, the nonmagnetic intermediatelayer has the thickness thereof is set that an antiferromagneticcoupling force may be generated between the adjacent ferromagneticlayers, in order to obtain a read back signal when a signal field isapplied in the same direction to each magnetic layer. In the presentembodiment, the GMR nonmagnetic intermediate layer 5 has the thicknessthereof set at 3 nm, for example, for the purpose of generating aferromagnetic coupling force between the first and the second GMRferromagnetic layer 4 a and 4 b. Owing to this ferromagnetic couplingforce, the magnetizations of the first and the second GMR ferromagneticlayers 4 a and 4 b are arranged in substantially equal direction withthe signal magnetic field in a state of zero.

For the first and the second signal magnetic field detectingferromagnetic layer 3 a and 3 b, it is desirable to use amorphous filmssuch as a CoZrNb film and a CoFeBc film, microcrystalline nitride filmssuch as a FeZrN film and a FeTaN film, microcrystalline carbide filmssuch as a FeTaC film and a FeZrC film, and alloy films such as a Fe—SiOheteroamorphous film and a NiFeX (wherein X stands for such metallicelements as Nb, Cr, Ta, Zr, Rh, Pd, Ru, Mo, and Cu). These films possesshigher permeability than the GMR ferromagnetic layers 4 a and 4 bmentioned above and, at the same time, possess high resistance exceeding100 μΩcm, for example, which is enough to prevent the degradation ofsensitivity by the partial sense current flow to the signal magneticfield detecting ferromagnetic layers 3 a and 3 b.

Though the thickness of the signal magnetic field detectingferromagnetic layers 3 a and 3 b is not particularly limited, it isdesired to be greater than that of the GMR ferromagnetic layers 4 a and4 b. Owing to the greater thickness, the detection of signal magneticfields is facilitated because the magnetic effects which the exchangecoupling thereof with the GMR ferromagnetic layers 4 a and 4 b manifestsas in degrading permeability are alleviated. Specifically, the signalmagnetic field detecting ferromagnetic layers 3 a and 3 are desired tohave a thickness in the approximate range of from 5 to 100 nm. If thesignal magnetic field detecting ferromagnetic layers 3 a and 3 b have anunduly small thickness, the rotation of the magnetizations of the GMRferromagnetic layers 4 a and 4 b in response to the rotation of themagnetizations of the signal magnetic field detecting ferromagneticlayers 3 a and 3 b will be attained with difficulty. If they have asmall thickness unduly instead, the permeability will tend to decreaseand the partial diversion of the shunt current into the signal magneticfield detecting ferromagnetic layers 3 a and 3 b will increase. Thesignal magnetic field detecting ferromagnetic layers 3 a and 3 b arespecifically formed of a CoZrNb film, a CoFeBC film, a FeZrN film, aFeTaN film, a FeTaC film, a FeZrC film, a Fe—SiO heteroamorphous film,or a NiFeX film which has a thickness of about 20 nm.

Then, the laminated structure consisting of the first GMR ferromagneticlayer 4 a, the GMR nonmagnetic intermediate layer 5, and the second GMRferromagnetic layer 4 b and constituting itself the GMR element 7 isformed of materials having lower wear resistance than the first and thesecond signal magnetic field detecting ferromagnetic layers 3 a and 3 b.As a result, the GMR element part 7 is made by polishing to recede fromthe opposed surface of the medium. The signal magnetic fields which aredirectly sensed by the GMR element part 7 grow weak and the gap lengthcan be regulated more precisely by the thickness of the GMR element part7. The recession of the GMR element part 7 from the opposed surface ofthe medium may be effected by selectively corroding the GMR element part7 by reactive ion etching or chemical dry etching, for example.

In the differential detection type MR head 1 of the structure mentionedabove, the first and the second GMR ferromagnetic layers 4 a and 4 b donot have the magnetizations thereof rotated directly by signal magneticfields. As the first and the second signal magnetic field detectingferromagnetic layers 3 a and 3 b have the magnetizations thereof rotatedby signal magnetic fields, the magnetizations of the first and thesecond GMR ferromagnetic layers 4 a and 4 b are rotated by the magneticcoupling across the interfaces in response to the rotation of the layers3 a and 3 b. As a result, the GMR element part 7 is made equal to asubstantial gap. The gap of a length (of the order of 10 to 100 nm, forexample) fit for the linear recording density, therefore, can be formed.The gap length of the differential detection type MR head 1 of thepresent embodiment is about 23 nm.

In the case of a perpendicular magnetic recording medium, for example,when the gap mentioned above is positioned as separated from themagnetization transition region of a magnetic recording medium 9 andsignal magnetic fields of equal directions are applied to the first andthe second signal magnetic field detecting ferromagnetic layers 3 a and3 b, the magnetizations of these layers 3 a and 3 b are rotated inmutually equal directions and the angle formed by the magnetizations ofthe first and the second GMR ferromagnetic layers 4 a and 4 b is notvaried after all. Consequently, no substantial variation of resistanceoccurs in the GMR element part 7. When the gap exists directly above themagnetization transition region of the magnetic recording medium 9 andsignal magnetic fields of mutual opposite directions are applied to thefirst and the second signal magnetic field detecting ferromagneticlayers 3 a and 3 b instead, the magnetizations of these layers 3 a and 3b are rotated in opposite directions and the angle formed by themagnetizations of the first and the second GMR ferromagnetic layers 4 aand 4 b is varied toward the antiparallel arrangement of magnetizations.As a result, the resistance of the GMR element part 7 is varied largelyand the detection of recorded information is attained.

In that way, the differential detection type MR head 1 of the embodimentcited the functions as a read head for displaying a differentialdetection type output response in the magnetization transition region ofthe magnetic recording medium 9. Unlike the differential detection typeMR head using the conventional AMR element, this MR head 1 produces adifferential detection by utilizing the resistance which variesproportionately to the angle formed by the magnetizations of the firstand the second GMR ferromagnetic layers 4 a and 4 b and consequentlyrealizes the reading with high sensitivity and high S/N ratio which hasnever been accomplished by the conventional AMR element. Further, thedetection of signals is stabilized because the magnetizations of thefirst and the second GMR ferromagnetic layers 4 a and 4 b occur insubstantially equal direction with the signal magnetic fields in a stateof zero. The differential detection type MR head 1 of the firstembodiment, therefore, is a read head which realizes, by the use of avery simple head structure, the adjustment of the gap length to thelength of the magnetization transition region of the magnetic recordingmedium 9 and the of high read sensitivity.

Then, In the GMR head using a spin valve structure, the magnetization ofeither of the GMR ferromagnetic layers is fixed by an antiferromagneticlayer. For this antiferromagnetic layer, generally, a FeMnantiferromagnetic layer which is capable of imparting a large biasmagnetic field enough to maintain stably the magnetization in the fixedstate in spite of an application of signal magnetic field is used. Sincethis FeMn antiferromagnetic layer is susceptible of corrosion, however,it forms a cause for degrading the durability of the MR head. Incontrast thereto, the differential detection type MR head 1 mentionedabove excels in durability because it has no use for the FeMnantiferromagnetic layer.

FIG. 2 through FIG. 5 are diagrams severally illustrating theconstructions of examples of the modification of the first embodimentmentioned above. Differential detection type MR heads 10, 11, 12, and 13shown therein are invariably adapted to apply a bias magnetic field tothe differential detection type MR elements 6 of their own. FIG. 2, forexample, depicts a construction having bias films 14 attached one eachto the opposite ends in the direction of track width of the differentialdetection type MR element 6. Then, FIG. 3 depicts a construction havingbias films 14 superposed on the opposite ends in the direction of trackwidth of the differential detection type MR element 6. FIG. 4 depicts aconstruction having bias films 14 interposed between the substrate 2 andthe MR element 6 below the opposite ends in the direction of track widthof the differential detection type MR element 6. FIG. 5 depicts aconstruction having the differential detection type MR element 6underlaid with a bias film 14.

The bias film 14 is formed of a hard ferromagnetic film such as, forexample, a CoPt film or an antiferromagnetic film such as, for example,a FeMn film or a NiO film. The differential detection type MR heads 10,11, 12, and 13 enable the magnetizations of the first and the second GMRferromagnetic layers 4 a and 4 b to be infallibly arranged insubstantially equal directions with signal magnetic fields in a state ofzero. They are further allowed to repress Barkhausen noise by deprivingthe respective ferromagnetic layers 3 a, 3 b, 4 a, and 4 b of a domainwall. Only the differential detection type MR head 13 shown in FIG. 5 isdesired to have a nonmagnetic layer interposed between the ferromagneticlayer 3 a and the bias film 14 when the bias wall 14 is formed of a hardferromagnetic film.

Next, the second embodiment of this invention will be described belowwith reference to FIG. 6.

In a differential detection type MR head 21 shown in FIG. 6, a first GMRferromagnetic layer 23 a adapted to have the magnetization thereofrotated by a signal magnetic field, a first GMR nonmagnetic intermediatelayer 24 a, a low-permeability ferromagnetic layer 25 not allowingsubstantial variation of the magnetization thereof by a signal magneticfield, a second GMR nonmagnetic intermediate layer 24 b, and a secondGMR ferromagnetic layer 23 b adapted to have the magnetization thereofrotated by a signal magnetic field similarly to the first GMRferromagnetic layer 23 a are sequentially superposed on a substrate 22.The laminated structure thus produced constitutes itself a GMR elementpart 26.

In this structure, the first GMR ferromagnetic layer 23 a, the first GMRnonmagnetic intermediate layer 24 a, and the low-permeabilityferromagnetic layer 25 jointly form a first GMR unit 27 a and thelow-permeability ferromagnetic layer 25, the second GMR nonmagneticintermediate layer 24 b, and the second GMR ferromagnetic layer jointlyform a second GMR unit 27 b. In addition, electrodes 27 a and 27 b forsupplying a sense current in the direction of track width (the directionof y in the diagram) are formed one each at the opposite ends of the GMRelement part 26. Thus, the differential detection type MR head 21 isconstructed.

For the first and the second GMR ferromagnetic layers 23 a and 23 b, itis desirable to use a NiFe alloy film, a CoFe alloy film, a CoFeNi alloyfilm and the like which excel in the spin-dependent scatting ability.The GMR ferromagnetic layers 23 a and 23 b are desired to have athickness in the approximate range of from 2 to 20 nm for the sake ofacquiring a large ratio of variation of the resistance. Then, for thefirst and the second GMR nonmagnetic intermediate layers 24 a and 24 b,it is desirable to use a Cu film, a Au film, a Ag film, and films ofalloys formed mainly of these metals which have low resistance fit forthe spin-dependent scattering. The GMR nonmagnetic intermediate layers24 a and 24 b are desired to have a thickness in the approximate rangeof from 1 to 10 nm for the sake of acquiring a large ratio of variationof the resistance. In the second embodiment, a NiFe alloy film, a CoFealloy film, or a CoFeNi alloy film having a thickness of 8 nm is usedfor the first and the second GMR ferromagnetic layers 23 a and 23 b anda Cu film, a Au film, a Ag film, a film of an alloy of such a metal andthe like, having a thickness of 3 nm is used for the first and thesecond GMR nonmagnetic intermediate layer 24 a and 24 b.

For the low-permeability ferromagnetic layer 25, a ferromagneticmaterial such as Co or a Co type alloy such as CoPt which excels in thespin-dependent scattering ability and allows impartation of highcoercive force and large uniaxial magnetic anisotropy can be used. Thislayer 25 is desired to have a thickness in the approximate range of from1 to 40 nm for the sake of acquiring a large ratio of variation of theresistance. In the present embodiment, the low-permeabilityferromagnetic layer 25 is formed of a CoPt film which has a thickness of20 nm and a coercive force of 20 kA/m (permeability =10). If anantiferromagnetic film rich in resistance and deficient in thespin-dependent scattering ability is used in the place of thelow-permeability ferromagnetic layer 25 in this case, the ratio ofvariation of the resistance is degraded markedly because this filmshatters the spin information of the GMR element part 26. When thelow-permeability ferromagnetic layer 25 is formed of Co or CoPt, itallows a large ratio of variation of the resistance.

The direction of the magnetization M_(a1) of the low-permeabilitysubstantially coincides with the direction of track width as shown inFIG. 7 irrespectively of the presence or the absence of a signalmagnetic field. Further, the direction of the magnetization M_(a1) ofthe low-permeability ferromagnetic layer 25 is stabilized substantiallyto resist a signal magnetic field when the layer 25 is endowed withheightened coercive force or increased uniaxial magnetic anisotropy. Themagnetizations M_(a2) and M_(a3) respectively of the first and thesecond GMR ferromagnetic layers 23 a and 23 b have their directionsrotated by a magnetic field which is generated by a sense current whilethe signal magnetic field is substantially in a state of zero.Specifically, this rotation occurs in the plus z direction in the caseof the first GMR ferromagnetic layer 23 a and in the minus z directionin the case of the second GMR ferromagnetic layer 23 b.

When signal magnetic fields of equal directions such as, for example,the plus z directions flow into the first and the second GMRferromagnetic layers 23 a and 23 b, the resistance increases in thefirst GMR unit 27 a because the angle formed by the magnetizationsM_(a2) and the magnetizations M_(a1) increases. The resistance in thesecond GMR unit 27 b decreases because the angle formed by themagnetizations M_(a2) and the magnetizations M_(a1) converselydecreases. The overall resistance in the GMR element part 26, therefore,is not varied.

When signal magnetic fields of opposite directions flow into the firstand the second GMR ferromagnetic layers 23 a and 23 b, the resistance inthe first GMR unit 27 a and that in the second GMR unit 27 b bothincrease or decrease because the angle formed by the magnetizationM_(a2) and the magnetization M_(a1) and the angle formed by themagnetization M_(a3) and the magnetization M_(a1) both increase ordecrease. As a result, the resistance of the GMR element part 26 islargely varied. The detection of a signal by the differential detection,therefore, is attained because the resistance of the GMR element part 26is amply varied by a signal magnetic field only when signal magneticfields of opposite directions are applied to the first and the secondGMR element part 26.

For the sake of enlarging the linear response region with thedifferential detection of the nature above-described, it is desirable toset the angles of rotation of the magnetizations M_(a2) and themagnetization M_(a3) produced by the sense current at about +45° andabout −45° respectively from the direction of track width (the ydirection in the diagram). This setting of the angles can beaccomplished by suitably selecting the magnitude of the sense current,the thicknesses of the component layers 23 a, 23 b, 24 a, 24 b, and 25,the magnitude of resistivity, and other factors.

The differential detection type MR head 21 of the embodiment describedabove functions as a read head which exhibits a defferential detectiontype output response in the magnetization transition region of themagnetic recording medium 9 as described above. Unlike the defferentialdetection type MR head using the conventional AMR element, this MR head21 produces a differential detection by utilizing the resistance whichvaries proportionately to the angle formed by the magnetizations of thefirst and the second GMR unit 27 a and 27 b and consequently realizesthe reading with high sensitivity and high S/N ratio which has neverbeen accomplished by the conventional AMR element. Further, thedifferential detection type MR head 21 can regulate the gap to a lengthfit for the magnetization transition region of the magnetic recordingmedium 9 with the interval between the two GMR ferromagnetic layers 23 aand 23 b.

In order for the differential detection type MR head 21 of theconstruction described above to accomplish the detection of a signalstably at a high S/N ratio by the differential detection, it isimportant that the magnetization M_(a1)of the low-permeabilityferromagnetic layer 25 will be prevented from being varied by a signalmagnetic field without causing the spin-dependent scattering ability tobe degraded. By the adoption of at least one of the structures (a)through (c) shown below, the magnetization M_(a1) of thelow-permeability ferromagnetic layer 25 can be stabilized.

(a) The component layers 23 a, 23 b, 24 a, 24 b, and 25 of the GMRelement part 26 have their depths (the widths in the z direction in thediagram) finally adjusted by a polishing to be given from the opposedsurface side of the medium. Soft magnetic films of high hardness enoughto defy the polishing are disposed one each outside the first and thesecond GMR ferromagnetic layers 23 a and 23 b. Owing to thisarrangement, at least the low-permeability ferromagnetic layer 25 iscaused to recede from the opposed surface of the medium. As a result,the magnetization M_(a1) gains in stability because the intensity of thesignal magnetic field applied to the low-permeability ferromagneticlayer 25 is consequently weakened. When the structure of this kind isadopted, a ferromagnetic material which excels in the spin-dependentscattering ability is used as described above for the low-permeabilityferromagnetic layer 25. As concrete examples of the soft magnetic filmof high hardness mentioned above, the Fe type and the Co type nitridefilms and the Co type amorphous films may be cited. The soft magneticlayer is desired to have a thickness in the approximate range of from 1to 50 nm.

The decrease of the sensitivity due to the recession of thelow-permeability ferromagnetic layer 25 in this case is slight becausethe soft magnetic film of high hardness mentioned above enables anecessary signal magnetic field to be drawn to the GMR element part 26,though more or less weakly as compared with the vicinity of the medium.If the soft magnetic film of high hardness has unduly low resistance,however, the ratio of variation of the resistance will possibly belowered because the sense current flows into the soft magnetic film. Itis, therefore, desirable to use for the soft magnetic film of highhardness a film having higher resistivity than the GMR ferromagneticlayers 23 a and 23 b.

The aforementioned recession of the low-permeability ferromagnetic film25 from the opposed surface of the medium can be equally accomplished byselectively etching the low-permeability ferromagnetic layer 25. The dryetching such as, for example, the so-called CDE may be utilized for thepurpose of this selective etching.

(b) Generally, more often than not a film of high coercive force and aferromagnetic film having large magnetic anisotropy have no fullysatisfactory spin-dependent scattering ability. To correct this defect,ferromagnetic films excelling in the spin-dependent scattering abilityare interposed one each between the low-permeability ferromagnetic layer25 and the first and the second GMR nonmagnetic intermediate layers 24 aand 24 b. owing to the adoption of this structure, the coercive forceand the magnetic anisotropy of the low-permeability ferromagnetic layer25 can be augmented without a sacrifice of the high ratio of variationof the resistance. Specifically, the low-permeability ferromagneticlayer 25 is formed of such a hard ferromagnetic film as a CoNiTa alloyfilm or a CoPtCr alloy film which does not possess a very highspin-dependent scattering ability and measures about 20 nm in thicknessand Co films which excel particularly in the spin-dependent scatteringability and have a thickness in the approximate range of from 1.5 to 5nm are interposed one each in the interfaces between thelow-permeability ferromagnetic film 25 and the first and the second GMRnonmagnetic intermediate layers 24 a and 24 b.

(c) The low-permeability ferromagnetic layer 25 is formed of anartificial lattice film which is produced by alternately superposingferromagnetic films and nonmagnetic films and consequently enabled togenerate an antiferromagnetic coupling between the adjacentferromagnetic films across the nonmagnetic films. The artificial latticefilm mentioned above is desired to have the magnitude of theantiferromagnetic coupling so controlled as to surpass the saturatedmagnetic field. As a concrete structure of the artificial lattice film,the film obtained by alternately superposing Co films of a thickness inthe approximate range of from 0.5 to 5 nm and Cu films or Ru films of athickness in the approximate range of from 0.5 to 5 nm may be cited.Also by this structure, the stability of the direction of themagnetization of the low-permeability ferromagnetic layer 25 relative tothe signal magnetic field can be heightened.

By adopting the structures (a) through (c) above-described, the readback signals with a high S/N ratio by a further stabilized differentialdetection can be realized.

Next, the third embodiment of this invention will be described belowwith reference to FIG. 8.

In a differential detection type MR head 31 shown in FIG. 8, a first GMRferromagnetic layer 33 a adapted to have the magnetization thereofrotated by a signal magnetic field, a first GMR nonmagnetic intermediatelayer 34 a, a first low-permeability ferromagnetic layer 35 a adapted tohave the direction of the magnetization thereof not substantially variedby a signal magnetic field, a separating nonmagnetic intermediate layer36 adapted to weaken a ferromagnetic coupling between adjacentferromagnetic layers 35 a and 35 b, a second low-permeabilityferromagnetic layer 35 b, a second GMR nonmagnetic intermediate layer 34b, and a second GMR ferromagnetic layer 33 b are sequentially superposedin the order mentioned on a substrate 32. The laminated structureconsequently obtained constitutes itself a GMR element part 7.

The first GMR ferromagnetic layer 33 a, the first GMR nonmagneticintermediate layer 34 a, and the first low-permeability ferromagneticlayer 35 a jointly form a first GMR unit 38 a and the secondlow-permeability ferromagnetic layer 35 b, the second GMR nonmagneticintermediate layer 34 b, and the second GMR ferromagnetic layer 33 bjointly form a second GMR unit 38 b. Further, electrodes 39 a and 39 bfor supplying a sense current in the direction of track width (the ydirection in the diagram) are formed one each at the opposite ends of aGMR element part 37. Of these components, the differential detectiontype MR head 31 is composed.

For the first and the second GMR ferromagnetic layers 33 a and 33 b andthe first and the second GMR nonmagnetic intermediate layers 34 a and 34b, the same materials and the same thicknesses as mentioned above withrespect to the second embodiment may be adopted. Likewise for the firstand the second low-permeability ferromagnetic layers 35 a and 35 b, thesame material and the same thickness as mentioned above with respect ofthe low-permeability ferromagnetic layer of the second embodiment can beadopted.

For the separating nonmagnetic intermediate layer 36, it is desirable touse a nonmagnetic film adapted especially for the spin-dependentscattering similarly to the first and the second GMR nonmagneticintermediate layer 34 a and 34 b for the purpose of obtaining a largeratio of variation of the resistance without disrupting the spininformation. For this film, such low resistance as fits thespin-dependent scattering is not always necessary. It is desirable touse such a nonmagnetic film as markedly weakens the ferromagneticcoupling between the first and the second low-permeability ferromagneticlayers 35 a and 35 b. When the dominant consideration resides inweakening the ferromagnetic coupling between the ferromagnetic layers 35a and 35 b, therefore, the separating nonmagnetic layer 36 may be formedof such a nonmagnetic insulating film as a SiO₂ film or an Al₂ ₃ film,for example. In cases where the separating nonmagnetic intermediatelayer 36 is desired to have an increased thickness for the sake ofadjusting the gap length, the degradation of the ratio of variation ofthe resistance due to the partial diversion of the sense current to theseparating nonmagnetic intermediate layer 36 can be prevented by theadoption of the nonmagnetic insulating film. Further, since theseparating nonmagnetic intermediate layer 36 is destined to serve as afoundation for the low-permeability ferromagnetic layer 35 b, such anonmagnetic metallic film as a Cr film or a Ta film which is adapted forthe impartation of high coercive force and high uniaxial magneticanisotropy to the low-permeability ferromagnetic layer 35 b may be used.The thickness of the separating nonmagnetic intermediate layer 36 may besuitably set in consideration of the material to be selected. For theadjustment of the gap length, the thickness is desired to be in theapproximate range of from 0.5 to 100 nm.

In cases where the differential detection type MR head 31 does notparticularly call for a high recording density, the gap length, whenenlarged, brings about the advantage of improving the read sensitivitybecause the signal magnetic field is extended throughout the entirevolume of the GMR element part 37. When the separating nonmagneticintermediate layer 36 has low resistivity, however, the sense currenttends to flow readily to the intermediate layer 36 and, meanwhile, theread sensitivity declines. When the thickness of the separatingnonmagnetic intermediate layer 36 is to be increased, therefore, it isdesirable to form the separating nonmagnetic intermediate layer 36 witha material having high resistivity.

The magnetization M_(b1) of the first low-permeability ferromagneticlayer 35 a extends in the direction perpendicular (the plus z directionin the diagram) to the opposed surface of the medium. In contrastthereto, the magnetization M_(b2) of the second low-permeabilityferromagnetic layer 35 b extends in the direction differing by 180° (theminus z direction in the diagram) from that of the firstlow-permeability ferromagnetic layer 35 a. The magnetizations in thedirections differing by 180° as described above can be realized asfollows.

First, the coercive forces H_(c1) and H_(c2) of the two low-permeabilityferromagnetic layers 35 a and 35 b are differentiated as by varying thefilm-forming conditions or superposing the films on differentfoundations. Incidentally, in the present embodiment, since thelow-permeability ferromagnetic layer 35 a superposed on the nonmagneticlayer 34 a acquires high coercive force with difficulty, the relationH_(cl)<H_(c2) inevitably arises. Then, the magnetization is effected byapplication of a magnetic field greater than the coercive force H_(c2),the magnetic field is nulled, and the magnetization is again effected byapplication of a magnetic field intermediate between H_(c1) and H_(c2)in the opposite direction. Particularly by using for the separatingnonmagnetic intermediate layer 36 a Cr film or a Ta film which isadapted for the impartation of high coercive force and high uniaxialmagnetic anisotropy to the second low-permeability ferromagnetic layer35 b as described above, the second low-permeability ferromagnetic layer35 b is easily allowed to acquire large coercive force as compared withthe first low-permeability ferromagnetic layer 35 a on the GMRnonmagnetic intermediate layer 34 a.

When the first and the second low-permeability ferromagnetic layers 35 aand 35 b are magnetized as described above, they are at an advantage inacquiring further enhanced stability to resist a signal magnetic fieldbecause they are each made to generate a magnetostatically couplingmagnetic field in the direction of intensifying the direction ofmagnetization. In addition, when the first and the secondlow-permeability ferromagnetic layer 35 a and 35 b are magnetizedrespectively in the plus z direction and the minus z direction, themagnetizations M_(bs) and M_(b4) of the first and the second GMRferromagnetic layers 33 a and 33 b are rotated in the plus z directionor the minus z direction from the direction of track width, depending onthe relevant signal magnetic fields, with the result that the resistanceis linearly varied as shown in FIG. 10 in conformity with the rotation.In FIG. 10, the symbol H_(s) ⁺ represents the magnetic field for causingthe magnetization to be extended in the plus z direction and the symbolH_(s−) represents the magnetic field for causing the magnetization to beextended in the minus z direction.

As a result, the linear variation of the resistance is obtained and thedetection of a signal of minor distortion and a high S/N ratio isaccomplished without requiring the magnetizations M_(b3) and M_(b4) ofthe first and the second GMR ferromagnetic layer 33 a and 33 b to berotated substantially in the ±45° directions by the sense current. Inother words, for the purpose of obtaining a wide range of linearresponse, it is desirable to turn the magnetizations M_(b3) and M_(b4)of the first and the second GMR ferromagnetic layer 33 a and 33 bsubstantially in the direction of track width (the y direction in thediagram) with the signal magnetic fields in a state of zero by utilizingthe form magnetic anisotropy and the induced magnetization anisotropyformed by the film formation in the magnetic field and/or applying abias field to the track width direction as is shown in FIGS. 2 to 5.

According to the structure described above, when signal magnetic fieldsof equal directions such as, for example, the plus z directions areapplied to the first and the second GMR ferromagnetic layer 33 a and 33b, the resistance decreases in the first GMR unit 38 a because themagnetizations of the first GMR ferromagnetic layer 33 a and the firstlow-permeability ferromagnetic layer 35 a are ferromagnetically arrangedas clearly noted from FIG. 10. The resistance conversely increases inthe second GMR unit 38 b because the magnetizations of the second GMRferromagnetic layer 33 b and the second low-permeability ferromagneticlayer 35 b are antiferromagnetically arranged. The variations of theresistance by the two GMR units 38 a and 38 b, therefore, are offset andthe overall resistance of the GMR element part 37 as a whole is notvaried.

When signal magnetic fields of opposite directions are applied to thefirst and the second GMR ferromagnetic layers 33 a and 33 b,specifically a signal magnetic field of the plus z direction to thefirst GMR ferromagnetic layer 33 a and a signal magnetic field of theminus z direction to the second GMR ferromagnetic layer 33 b, theresistance in the first GMR unit 38 a decreases because themagnetizations of the first GMR ferromagnetic layer 33 a and the firstlow-permeability ferromagnetic layer 35 a are arranged ferromagneticallyand the resistance in the second GMR unit 38 b likewise decreasesbecause the magnetizations of the second GMR ferromagnetic layer 33 band the second low-permeability ferromagnetic layer 35 b are arrangedferromagnetically. As a result, the differential detection typedetection of magnetic fields is attained because the overall resistanceof the GMR element part 37 is amply varied.

The differential detection type MR head 31 of the third embodimentdescribed thus far functions as a read head which displays adifferential detection type output response in the magnetizationtransition region of the magnetic recording medium 9 as described above.This differential detection type MR head 31, like the differentialdetection type MR head 21 of the second embodiment described previously,produces the differential detection by utilizing the resistance whichvaries proportionately to the angle formed by the magnetizations in thefirst and the second GMR unit 38 a and 38 b and, therefore, realizes thereading with high sensitivity and a high S/N ratio which has never beenattained by the conventional AMR element. Further, in the differentialdetection type MR head 31, the gap length finely adapted for the linearrecording density can be set because the interval between the two GMRferromagnetic layers 33 a and 33 b can be adjusted as desired by thethickness of the separating nonmagnetic intermediate layer 36.

Then, the differential detection type MR head 31 of the structuredescribed above, like the differential detection type MR head 21 of thesecond embodiment described previously, is desired to adopt at least oneof the structures of (a) through (c) described above so that thespin-dependent scattering ability may not be degraded and themagnetizations M_(b1) and M_(b2) of the first and the secondlow-permeability ferromagnetic layers 35 a and 35 b may not be varied bya signal magnetic field. These structures have been already describedspecifically.

The differential detection type MR heads 21 and 31 respectively of thesecond and the third embodiment above-described may have ferromagneticlayers for the detection of signal magnetic fields disposed one eachoutside the GMR ferromagnetic layers in the same manner as in the firstembodiment.

Next, the fourth embodiment of this invention will be described belowwith reference to FIG. 11.

In a differential detection type MR head 41 shown in FIG. 11, a firstlow-permeability ferromagnetic layer 43 a, a first GMR nonmagneticintermediate layer 44, a first GMR ferromagnetic layer 45 a, aseparating nonmagnetic intermediate layer 46, a second low-permeabilityferromagnetic layer 43 b, a second GMR nonmagnetic intermediate layer 44b, and a second GMR ferromagnetic layer 45 b are sequentially superposedin the order mentioned on a substrate 42. The laminated structure thusformed constitutes itself a GMR element part 47.

The first low-permeability ferromagnetic layer 43 a, the first GMRnonmagnetic intermediate layer 44 a, and the first GMR ferromagneticlayer 45 a jointly form a first GMR unit 48 a and the secondlow-permeability ferromagnetic layer 43 b, the second GMR nonmagneticintermediate layer 44 b, and the second GMR ferromagnetic layer 45 bjointly form a second GMR unit 48 b. Further, electrodes 49 a and 49 bfor supplying a sense current in the direction of track width (the ydirection in the diagram) are formed one each at the opposite ends ofthe GMR element part 47. These components complete the differentialdetection type MR head 41.

The materials and the thicknesses of the component layers of the GMRelement part 47 are similar to those of the component layers of thedifferential detection type MR head 31 of the third embodiment describedabove. Further, for the sake of augmenting the coercive force and theuniaxial magnetic anisotropy of the first low-permeability ferromagneticlayer 43 a, a nonmagnetic film made of Cr or Ta may be interposedbetween the substrate 42 and the first low-permeability ferromagneticlayer 43 a.

With this differential detection type MR head 41, like the differentialdetection type MR head 31 of the third embodiment, the same differentialdetection type detection of a magnetic field as is attained by the thirdembodiment can be realized by causing the magnetizations M_(c1) andM_(c2) of the first and the second low-permeability ferromagnetic layers43 a and 43 b to be respectively turned in the plus z direction and theminus z direction as shown in FIG. 12. According to this structure, forthe separating nonmagnetic intermediate layer 46 which is destined toserve as a foundation for the first low-permeability ferromagnetic layer43 a and as a foundation for the second low-permeability ferromagneticlayer 43 b, such a Cr film as is adapted for heightening the coerciveforce and the uniaxial magnetic anisotropy of the first and the secondlow-permeability ferromagnetic layer 43 a and 43 b can be used. The useof this Cr film is at an advantage in stabilizing the magnetizations ofthe first and the second low-permeability ferromagnetic layers 43 a and43 b to resist the magnetic field of the medium. The fact that amagnetostatically coupling magnetic field is generated between the firstand the second low-permeable ferromagnetic layer 43 a and 43 b and thestability to resist signal magnetic fields is further improved has anexact equivalent in the third embodiment. The desire to impart adeviation of 180° between the directions of the magnetizations of thefirst and the second low-permeability ferromagnetic layer 43 a and 43 bmay be satisfied, in the same manner as in the third embodiment, byvarying the film-forming conditions of the low-permeabilityferromagnetic layer 43 a and 43 b or by using different foundationstherefor.

Then, the fifth embodiment of this invention will be described belowwith reference to FIG. 13.

In a differential detection type MR head 52 shown in FIG. 13, a firstsignal magnetic field detecting ferromagnetic layer 53 a, a granulartype ferromagnetic intermediate layer 54 intended as an intermediatelayer, and a second signal magnetic field detecting magnetic layer 53 bare sequentially superposed in the order mentioned on a substrate 52 toform a differential detection type MR element 55. Further, electrodes 56a and 56 b for supplying a sense current are formed one each at theopposite ends of the differential detection type MR element 55.

The granular type ferromagnetic intermediate layer 54 has a phaseseparation into a magnetic region 54 a and a nonmagnetic region 54 b. Inthe magnetic region 54 a, the resistance generated therein decreases inproportion to the increase of the components having magnetizationsarranged in equal directions and increases in proportion to the increaseof the components of antiparallel magnetizations. In the presentdifferential detection type MR head 51, therefore, the granular typeferromagnetic intermediate layer 54 functions as a GMR element part. Thegranular type ferromagnetic intermediate layer 54 has a thickness ofabout 30 nm, for example, and the magnetic region 54 a thereof is formedof a magnetic material having Co, Ni, Fe, etc. as a main componentthereof, and the nonmagnetic region 54 b thereof is formed of anonmagnetic material such as of Cu, Au, Ag, alloys thereof, etc.

The granular type ferromagnetic intermediate layer 54 is desired to bemagnetized with a ferromagnetic field or to be provided with a biasfilm, as in any of the structures shown in FIG. 2 through FIG. 5, so asto arrange the magnetizations of the magnetic region 54 a insubstantially equal directions with the signal magnetic field in a stateof zero. As a result, the granular type ferromagnetic intermediate layer54 equals a substantial gap and permits formation of a gap of a suitablelength in the approximate range of from 10 to 100 nm.

When the granular type ferromagnetic intermediate layer 54 destined toserve as a gap is positioned as separated from the magnetizationtransition region of the magnetic recording medium 9 and signal magneticfields of equal directions are applied to the first and the secondsignal magnetic field detecting ferromagnetic layer 53 a and 53 b, themagnetizations of these layers 53 a and 53 b are rotated in mutuallyequal directions and the magnetizations within the magnetic region 54 aof the granular type ferromagnetic intermediate layer 54 areconsequently rotated in the equal directions and the angle formed by themagnetizations is not varied after all. In the granular typeferromagnetic intermediate layer 54, therefore, the resistance is notvaried substantially. When the granular type ferromagnetic intermediatelayer 54 destined to serve as a gap exists directly above themagnetization transition region of the magnetic recording medium 9 andsignal magnetic fields of mutual opposite directions are applied to thefirst and the second signal magnetic field detecting ferromagnetic layer53 a and 53 b, the magnetizations of these layers 53 a and 53 b arerotated in mutual opposite directions near the interfaces of theferromagnetic layers 53 a and 53 b and, as a result, the magnetizationsin the magnetic region 54 a within the granular type ferromagneticintermediate layer 54 have increased antiparallel components. As aresult, the resistance of the granular type ferromagnetic intermediatelayer 54 increases and permits detection of the recorded information.

The differential detection type MR head 51 of the present embodiment,like the equivalent in any of the embodiments cited above, functions asa read head for displaying a differential detection type output responsein the magnetization transition region of the magnetic recording medium9. Then, it produces the differential detection by utilizing theresistance which varies with the angle formed by the magnetizations inthe magnetic region 54 a of the granular type ferromagnetic layer 54and, therefore, realizes the reading with high sensitivity and a highS/N ratio which has never been attained by the conventional AMR element.Further, by setting the gap length suitably with the thickness of thegranular type ferromagnetic intermediate layer 54 as described above,the reading of such notably high linear recording density as not morethan 0.1 μm can be realized with high sensitivity.

As clearly demonstrated by the embodiments cited above, the differentialdetection type MR head of this invention is capable of stably obtaininga differential detection type output response and allows realization ofthe reading of notably high linear recording density with highsensitivity.

What is claimed is:
 1. A differential detection magnetoresistance headcomprising: a magnetoresistance element part having a laminatedstructure, the magnetoresistance element part having a resistance andcomprising: a pair of ferromagnetic layers, each having a magnetization,and an intermediate layer interposed between said pair of ferromagneticlayers, said intermediate layer being formed of an electricallyconductive material suitable for spin-dependent scattering; and a pairof signal magnetic field detecting ferromagnetic layers, each of thesignal magnetic field detecting ferromagnetic layers being disposedoutside each of the ferromagnetic layers, wherein the resistance of saidmagnetoresistance element part is varied when the magnetization of eachof the ferromagnetic layers is changed to an opposite direction bysignal magnetic fields, and wherein recorded information on a magneticmedium is detected utilizing the variation of resistance based on agiant magnetoresistance effect due to the spin-dependent scattering insaid magnetoresistance element part, said pair of ferromagnetic layersis recessed from said pair of signal magnetic field detectingferromagnetic layers relative to a surface of the magnetoresistance headfacing the magnetic medium.